The phrase "won't hold water" typically means something that is not logical or credible. When trying to find antonyms for this phrase, one can consider words that describe something that is valid, reasonable, or acceptable. Some possible antonyms for "won't hold water" include reliable, valid, sound, logical, credible, convincing, and substantial. These antonyms can be used to describe arguments, statements, or evidence that are strong and supportable, rather than being weak or fallacious. By using these antonyms, one can effectively communicate the opposite of the concept conveyed by the phrase "won't hold water.